Towards Safer Li-Ion Batteries: A Study on Electrolyte Solvation and Dynamics with the Incorporation of Low Volatility Co-Solvents

Abstract

Molecular dynamics (MD) simulations were employed to investigate how the content and type of co-solvents influence the solvation structure and transport properties of lithium ions (Li+) in electrolytes. Our focus was on lithium hexafluorophosphate (LiPF6) at a concentration of 1.0 M in a carbonate-based solvent composed of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a 1:1 mixing ratio. Low-volatility co-solvents, including tetramethylene sulfone (TMS), dimethyl sulfoxide (DMSO), fluoroethylene carbonate (FEC), and succinonitrile (SN), were introduced into the electrolytic matrix at concentrations of 0, 10, 25, 50, 75, and 100 wt.%. Li+ dynamics were notably influenced by these factors. The highest Li+ transference number was observed at a 25 wt.% concentration for each co-solvent, particularly with 25 wt.% DMSO, resulting in the highest ionic conductivity (14.13 mS/cm) and Li+ transference number (0.47). In this system, the PF6 - anion refrains from joining the initial solvation shell of Li+. This is attributed to the higher donor number of DMSO compared to TMS, FEC, and SN, leading to a weakening of electrostatic interactions. These findings advance our comprehension of electrochemical principles in bulk electrolytes, providing insights for designing safer and more efficient lithium-ion batteries.